1. Field of the Invention
The present invention relates to an image forming apparatus, and particularly to a method for erasing data stored in a hard disk provided in an image forming apparatus.
2. Description of the Related Art
A state-of-the-art image forming apparatus such as copy machine, Multi-Function Peripheral (hereinafter, referred also to “MFP”) combining the functions of printing, copying, faxing, etc., takes advantage of digital technologies. Further, information on a print job, etc., is stored in a hard disk apparatus that contains a hard disk (HD) as a high capacity data storage medium and is incorporated in the image forming apparatus. If the apparatus incorporating an HD is discarded or sold, or returned to the tenant upon expiration of the lease, or temporarily transferred to an external vendor for repair, etc., there is a risk of leakage of confidential information stored in an HD.
Leakage of confidential information is the most critical social issue and in order to address this very critical issue, suppliers of the copy machine or MFP take countermeasure by encrypting information on a print job, etc., before storing the information in an HD. However, even when information is encrypted, the encrypted information is in some cases decrypted using decryption software.
In order to prevent leakage of confidential information stored in an HD when the printer or MFP is discarded, conventionally, the HD is mechanically destroyed or data stored in an HD is eliminated by placing the HD in a strong magnetic field, or all of used areas of an HD are overwritten with useless data. Among the above-mentioned methods, the method for destroying an HD mechanically can be employed when the apparatus is discarded, but is not suitable for other cases, for example, where the apparatus is sold. Further, the method for exposing an HD to a strong magnetic field requires a special equipment and therefore the implementation of the method is difficult in practice. For these reasons, if the copy machine, etc., or MFP incorporating an HD is discarded or sold, or returned to the tenant upon expiration of the lease, or temporarily transferred to an external vendor for repair, etc., a method for overwriting all of used areas of an HD with useless data has been widely employed. However, this method causes a serious problem. That is, the storage capacity of an HD incorporated into the copy machine, etc., or MFP is as large as a few tens of Gigabytes and in order to overwrite all of areas of an HD having a storage capacity of 50 Gigabytes with useless data, it takes as much as about one hour. Further, the storage capacity of an HD tends to increase and the problem will become more and more serious.
Moreover, for example, when MFP captures the image of an original document, stores the image data temporarily in an HD, retrieves the image data from the HD, and prints out the image data, the image data is still stored in the HD even after the image data has been printed out. More specifically, the image data is stored in a predetermined area of the HD and is still stored in the HD until another original document is read and overwritten with the data of another original document. Accordingly, when the HD is removed from MFP, etc., and information contained in the HD is analyzed, the information contained in the HD will be revealed. A method of avoiding this problematic situation is disclosed in Japanese Patent Unexamined Publication No. 9-284572 in which image data that has been printed out eliminating the need for the image data to be stored in an HD is erased in order. However, a process for erasing image data and a process for scanning the image of an original document, writing image data into an HD, and retrieving the image data from the HD cannot be concurrently performed. For this reason, when erasing of the image data is carried out, other processes have to wait until completion of the erasing of the image data, resulting in reduction in efficiency of other processes and decrease in user convenience. Therefore, what is needed is to reduce the time required in a process for erasing image data stored in an HD.